The active-matrix type liquid crystal display device is equipped with a liquid crystal layer held between a pair of substrates which counter mutually, and a display portion which consists of a plurality of display pixels arranged in the shape of a matrix. One of the pair of substrates includes scan lines arranged along with row lines of the display pixels, and signal lines arranged along with column lines of the display pixels in the matrix. An alignment state of the liquid crystal molecule contained in the liquid crystal layer is controlled by an electrical field impressed to the liquid crystal layer.
Recently, liquid crystal display devices such as an IPS (In-Plane Switching) mode type and a FFS (Fringe Field Switching) mode type using a lateral electrical field have been proposed. The IPS mode type and the FFS mode type include a plurality of first electrodes arranged in the matrix and a second electrode that counters the first electrodes on one of the substrates, and the state of an alignment of the liquid crystal molecule contained in the liquid crystal layer is controlled by the lateral electrical field generated between the first and second electrodes.
In the liquid crystal display, a line inversion driving method is proposed, in which the polarity of an impressed voltage to the liquid crystal layer for every scan line is inversed for preventing generation of a flicker phenomenon. When the line inversion driving method is adopted in the IPS mode or the FFS mode, the second electrode is arranged for every scan line, and the voltage supplied to the second electrode for every one-frame period is changed to either of the high (H) level and the low (L) level to inverse the polarity of the voltage impressed to the liquid crystal layer. In this structure, the alignment of the liquid crystal molecule contained in the liquid crystal layer is controlled by two kinds of voltages supplied to the second electrode and a picture signal sequentially written in the first electrode.
For example, when a power supply is turned off in the liquid crystal display device in a normally black mode, first, black data (picture signal corresponding to the black display) is written in all the display pixels based on a predetermined sequence in order to prevent disturbance of a screen by performing the black display. Then, the power supply to the liquid crystal panel is shut by turning off a power switch inserted in a power supply line after a predetermined time passes.
However, when two kinds of voltages with positive and negative are supplied to the second electrode, even if the black data is written in all the display pixels, the time for electric discharge of the high level common potential is different from that of the low level common potential after the power supply is turned off. Therefore, an incidental image, such as a lateral line shape may be generated.
Moreover, since the writing of the black data is sequentially performed by scan operation in every scan line like the writing of the normal display data, it takes time of at least one field period to write the black data in one screen. For this reason, the prior method can not respond to sudden power-off which occurs momentary. Accordingly, it was difficult to avoid the generation of the incidental lateral line.
A liquid crystal display device including an auxiliary capacitance coupled with a pixel capacitance and an auxiliary capacitance line for supplying a voltage to the auxiliary capacitance is proposed to make amplitude of the signal supplied to the signal lines small. Conventionally, a liquid crystal display device is proposed, in which the liquid crystal display device includes a low-voltage line to supply a low level voltage and a high-voltage line to supply a high voltage to the auxiliary capacitance line respectively, and a switching circuit to connect the auxiliary capacitance line with one of the low-level voltage line and the high-voltage line (refer to a Japanese Laid Open Patent Application No. 2009-104050).